1. Field of the Invention
The present invention relates to an air conditioner for a vehicle which heats or cools the interior of the vehicle by heating or cooling outside air or inside air, and specifically to an air conditioner suitable for use as a heat-pump type air conditioner mounted in an electric automobile.
2. Description of the Related Art
In a conventional air conditioner of this type, the air conditioner generally has a motor fan for drawing outside air from an outside-air inlet port and inside air from an inside-air inlet port and a heat pump unit for exchanging heat with air before discharging the air into the interior of the vehicle. When the interior of the vehicle is to be heated, the air is heated by the heat pump unit, when the interior of the vehicle is to be cooled, the air is cooled by the heat pump unit, and then the heat-exchanged air is supplied into the interior of the vehicle for air conditioning.
When the heating and cooling operation is automatically controlled, the control is performed based on a temperature calculated by the following equation (TAO: target temperature of discharged air). EQU TAO=Ks.multidot.Ts-Kr.multidot.Tr-Kam.multidot.Tam-Krad.multidot.Trad+C
In the above equation, "Ts" represents a temperature set by a user, "Tr" represents a temperature of the inside air, "Tam" represents a temperature of the outside air, "Trad" represents a value converted into a temperature value from an amount of solar radiation, "Ks" represents a set temperature factor, "Kr" represents an inside-air temperature factor, "Kam" represents an outside-air temperature factor, "Krad" represents a solar radiation factor and "C" represents a correction factor. These factors are selected as appropriate substantive values depending upon size of the interior space, etc.
Thus, the heating and cooling operation is selectively controlled based on the target temperature of discharged air, and the control of inlet air is performed at one of the outside-air mode and the inside-air mode.
In such a conventional air conditioner for vehicles, however, in a case where the outside-air mode is selected in the heating operation mode, even when the temperature of the outside air is very low and the load for the heating operation is great, the operation is continued utilizing only this low-temperature outside air. On the other hand, in a case where the outside-air mode is selected in the cooling operation mode, even when the temperature of the outside air is very high and the load for the cooling operation is great, the operation is continued utilizing only this high-temperature outside air. Therefore, the efficiency for heating and cooling operation relative to the load required for air conditioning of the interior of the vehicle is not good, such a condition is disadvantageous for saving energy, and particularly in an electric automobile, this causes a great reduction of the travel distance thereof.